为什么这个JS几秒后会跳转，求解正确的写法？

Question

<script type="text/javascript">function U_jump(Second, Url) {if (--Second > 0) {setInterval(U_jump(Second, Url),1000);}else {location.href = Url; }}window.onload(U_jump(10, "/swlogin.aspx"));</script>